This material is published in Scientific Reports (2013), the only definitive repository of the content that has been certified and accepted after peer review. doi:10.1038/srep02836.

Competitive environments sustain costly altruism with negligible assortment of interactions

C. Patrick Doncaster, Adam Jackson, and Richard A. Watson


Competition hinders the evolution of altruism amongst kin when beneficiaries gain at the expense of competing relatives. Altruism is consequently deemed to require stronger kin selection, or trait-selected synergies, or elastic population regulation, to counter this effect. Here we contest the view that competition puts any such demands on altruism. In ecologically realistic scenarios, competition influences both altruism and defection. We show how environments that pit defectors against each other allow strong altruism to evolve even in populations with negligible kin structure and no synergies. Competition amongst defectors presents relative advantages to altruism in the simplest games between altruists and defectors, and the most generic models of altruistic phenotypes or genotypes invading non-altruistic populations under inelastic density regulation. Given the widespread inevitability of competition, selection will often favour altruism because its alternatives provide lower fitness. Strong competition amongst defectors nevertheless undermines altruism, by facilitating invasion of unrelated beneficiaries as parasites.

Access to the full article at Scientific Reports.


Access Appendix S1. Graphical spread-sheet calculator in Microsoft Excel, for game theory on interactions amongst related individuals in competitive environments.

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